Safety assembly for fastener driving tool

ABSTRACT

A safety mechanism for a pneumatic fastener driving tool prevents operation of the tool when a nosepiece structure containing a fastener discharging opening is not disposed flush against and covered by a workpiece. This avoids &#39;&#39;&#39;&#39;free flight&#39;&#39;&#39;&#39; of power driven fasteners resulting from a tool being disposed at an angle adjacent an edge of a workpiece so that the fastener passes through only a portion of the workpiece. To accomplish this, the safety assembly includes two workpiece engaging members disposed on opposite sides of the nosepiece structure and coupled to opposite ends of a lever centrally fulcrumed on an operator for the tool firing control. Unless both members are elevated by engagement with the workpiece, the lever does not operate the control. To reduce the chances of tool operation when the tool is tipped in the plane of the workpiece engaging members, these members are so formed as to provide only point or small area contact with the workpiece.

States Patent 11 1 1 Oct. 2, 1973 1 SAFETY ASSEMBLY FOR FASTENERlUllRllVllNG TOUL [75 I Inventor: Bernard W. Geist, Melrose Park, 111.

[73] Assignee: Fastener Corporation, Franklin Park, Ill.

[22] Filed: May KS, 11972 [211 App]. No.: 253,449

[52] U.S. Cl. 227/8 [51] Int. [31 B27t 7/22 [58] Field of Search 227/7,8

[56] References Cited UNITED STATES PATENTS 3,162,097 12/1964 Allen etal. 227/130 X 3,198,412 8/1965 Roosa 227/8 Primary Examiner-Granville Y.Custer, Jr. Attorney-Richard D. Mason et a1.

[ ABSTRACT A safety mechanism for a pneumatic fastener driving toolprevents operation of the tool when a nosepiece structure containing afastener discharging opening is not disposed flush against and coveredby a workpiece. This avoids free flight" of power driven fasteners resulting from a tool being disposed at an angle adjacent an edge of aworkpiece so that. the fastener passes through only a portion of theworkpiece. To accomplish this, the safety assembly includes twoworkpiece engaging members disposed on opposite sides of the nosepiecestructure and coupled to opposite ends of a lever centrally fulcrumed onan operator for the tool firing control. Unless both members areelevated by engagement with the workpiece, the lever does not operatethe control. To reduce the chances of tool operation when the tool istipped in the plane of the workpiece engaging members, these members areso formed as to provide only point or small area contact with theworkpiece.

10 Claims, 7 Drawing Figures :iiii

SAFETY ASSEMBLY FOR FASTENER DRIVING TOOL This invention relates to afastener driving tool and, more particularly, to such a tool having anew and improved safety means for insuring that the fastener dischargingopening of the tool is disposed flush against a workpiece into which thefastener is to be driven.

Pneumatic and other types of power driven fastener driving tools havelong been provided with mechanical and/or pneumatic safety or touch-tripassemblies de' signed to prevent manually controlled operation of thetool unless and until the nosepiece structure of the tool through whichthe driven fastener is discharged is disposed against the workpiece.These arrangements commonly include a workpiece engaging element, eitherU-shaped or concentric with the nosepiece structure, which projectsdownwardly beyond the nosepiece to be elevated when the nosepiece ispressed against the workpiece. These elements Operate a pneumatic valveor a machanical linkage associated with the trigger actuated firingcontrol to permit the tool to be operated.

These workpiece engaging elements generally are rigid and eithersubstantially completely embrace the nosepiece (U.S. Pat. Nos. 3,572,572and 3,580,455) or extend almost completely across the width of the nosepiece (U.S. Pat. Nos. 3,172,124 and 3,194,324). These constructions aresuch that when the tool is inclined either in the plane of the tool orin a plane transverse to the plane of the tool the rigid workpieceengaging element is elevated sufficiently to release the tool foroperation even though the lower wall of, the nosepiece through which thestaple or nail is ejected is inclined or tipped relative to theworkpiece surface. This tipped position causes the fasteners to bedriven at an angle with respect to the workpiece.

When fasteners are driven under these conditions and if the fasteningoperation is being performed adjacent the edge ofa workpiece, thefastener such as a nail passes through only an edge portion of theworkpiece and then enters free flight. This occasions the possibility ofinjury to an operator or equipment and has, in some areas, led to workregulations forbidding the presence of more than a single tool operatorin an assembly area. The use of single point contact safety actuators insome prior tools (U.S. Pat. Nos. 3,056,964 and 3,252,641) preventstipping of the tool in a first plane, generally a plane transverse tothe plane of the tool, but not in the direction of elongation of thetool.

Accordingly, an object of the present invention is to provide a new andimproved fastener driving tool and, more specifically, a new andimproved safety assembly for such a tool.

A further object is to provide a safety assembly for a power actuatedfastener driving tool that requires the tool to be properly located withrespect to a workpiece before the tool can be operated.

Another object is to provide a safety assembly including independentlymovable workpiece engaging ele ments disposed on opposite sides of thefastener discharge opening to insure that the opening is placed againstthe workpiece before the tool can be operated.

Another object is to provide such a safety assembly in which theworkpiece engaging elements have point or small area contact with theworkpiece in a position immediately adjacent the fastener dischargingopening to insure that the safety cannot be released when the tool istipped relative to the workpiece.

In accordance with these and many other objects, an embodiment of theinvention comprises a pneumatic fastener driving tool formed by ahousing containing a power unit whose actuation is controlled by acontrol unit including a trigger operator and a safety operator, both ofwhich must be actuated to permit operation of the power unit. When thepower unit is operated, a fastener driving element or blade isreciprocated through a drive track in a nosepiece structure to drive astaple or nail supplied from a magazine assembly into a workpiece.

In accordance with the present invention, a safety assembly is providedwhich prevents operation of the tool or actuation of the control unitunless and until the surface of the nosepiece containing the fastenerdischarging opening is disposed against and in a flush relation with theworkpiece into which the fastener is to be driven. If the tool isdisposed in a tipped or canted relation to the workpiece in virtuallyany plane, the control unit cannot be actuated to effect operation ofthe power unit. To accomplish this, a safety assembly is providedincluding a pair of independently movable workpiece engaging elementsdisposed on opposite sides of the drive track or fastener dischargingopening. These workpiece engaging elements are coupled to a lever whichin turn is coupled to the safety operator so that the safety operatorcannot be actuated unless both of the workpiece engaging elements havebeen elevated by engagement with the workpiece. This insures that thenosepiece of the tool is flush against the workpiece in the plane of thetool. By providing the workpiece engaging elements with point or smallarea contact surfaces for engagement with the workpiece, it becomesdifficult to effect full actuation of these elements when the tool istipped in a plane transverse to the plane of the tool. Thus, the safetyoperator cannot be fully actuated in most circumstances when the tool istipped in any direction relative to the workpiece, and the possibilitythat a fastener will be driven through only a por tion of the workpieceand enter free flight" is materially and substantially reduced.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which;

FIG. 1 is a fragmentary side elevational view illustrating a pneumaticfastener driving tool embodying the present invention;

FIG. 2 is an end elevational view of the tool shown in FIG. 1illustrating a dualelement safety actuator assembly in a normalcondition;

FIG. 3 is an enlarged fragmentary sectional view taken along line 3-3 inFIG. 1;

FIG. 4 is an end elevational view similar to FIG. 2 illustrating thesafety assembly with one workpiece engaging element actuated;

FIG. 5 is an end elevational view similar to FIG. 4 and illustrating thesafety assembly with the other workpiece engaging element actuated;

FIG. 6 is an end elevational view similar to FIGS. 2, 4, and 5illustrating the safety assembly with both workpiece engaging elementsactuated; and

FIG. 7 is an exploded perspective view of the safety actuating assembly.

Referring now more specifically to FIGS. l and 2 of the drawings,therein is illustrated a fastener driving tool which is indicatedgenerally as W and which embodies the present invention. The tool it)includes a power unit (not shown) of a suitable type, such as apneumatic piston and cylinder, to which is attached a fastener drivingelement or driver for driving or setting fasteners, such as staples ornails, successively supplied to a drive track in a nosepiece structureindicated generally as 12 by a magazine assembly of conventionalconstruction indicated generally as M. To provide means for manuallycontrolling operation of the tool or the power unit in the tool it),there is provided a control unit indicated generally as 16. When amanually actuated trigger 13 forming a part of the assembly or unit i6is actuated, the power unit in the tool is rendered effective to drive afastener only when and if a safety assembly indicated generally as hasbeen fully actuated to indicate that the fastener discharging opening inthe lower end of the nosepiece structure I2 is against the workpieceinto which the fastener is to be driven. In accordance with the presentinvention, the safety assembly 2% is so designed that the control unit16 is inhibited to prevent actuation in response to operation of thetrigger 18 if the tool It) is tipped or canted with respect to theworkpiece.

The tool It) can be of any of the types well known in the art and caninclude, for example, a cylinder in which a piston coupled to the upperend of a driver blade is reciprocated by the selective admission ofpressurized fluid or compressed air by a main valve, the opening andclosing of which is controlled by the control unit 16. As an example,the tool can be constructed as shown and described in detail in US. Pat.No. 3,638,532. The control unit 16 can also be constructed as shown anddescribed in detail in this patent. In general, the control unit 16includes a housing 22 containing one or a number of valves forselectively controlling the admission of pressurized fluid to thecylinder of the power unit. When the trigger it; which is pivotallymounted on the housing 22 is actuated and when the safety assembly 26 isactuated, the power unit is rendered effective to operate through one ora plurality of cycles during which one or a plurality of fasteners aredriven.

To provide a means for controlling the effectiveness of the control unit16 in dependence on the condition of the safety assembly 24 the controlunit 116 includes a safety operator or an operator means 241 which, inthe control unit shown in the safety assembly shown in theabove-identified patent, comprises a valve stem. This stem 2 projectsfrom the lower wall of the housing 22 (FIG. 3). When the safety operator24, is in the lower position shown in FIGS. 1 and 3, the control unit H6is disabled. When the operator 24 is moved upwardly into the housing 22to the position shown in dashed outline in FIG. 6, the control unit 116is placed in a condition in which it can be operated by depression ofthe trigger E8.

The nosepiece structure 12 is secured to the lower end of a housing 26for the tool It), as by a plurality of machine screws 28. The nosepiecestructure 12 contains a drive track for reciprocably receiving thedriver element actuated by the power unit for driving nails or staplessupplied to the drive track from the magazine 14. The magazine 14includes a body portion lliA, the forward end of which is secured to andbetween rearwardly extending projecting portions or tabs 12A (FIGS. iiand 7) formed integral with the nosepiece structure 12. The lower end ofthe nosepiece structure 12 is provided with a downwardly and inwardlytapered portion indicated generally as 128 which terminates in agenerally planar workpiece engaging surface or portion 12C in which isdisposed a fastener discharging opening through which fasteners drivenout of the drive track enter the workpiece.

The actuating or operating means for the safety assembly 20 is slidablymounted on the nosepiece structure 12. This actuating assembly includesa pair of workpiece engaging elements or members 30 and 32 preferablyformed of bent wire stock and having a generally U-shaped configurationat their lower ends. Each of the elements 30 and 32 is formed with asomewhat V-shaped or pointed portion 30A, 32A at its lower end toprovide a point or small area contact with the workpiece. To providemeans for slidably supporting the elements 30 and 32 for independentmovement, the nosepiece structure 12 is provided with two pairs ofgenerally aligned slots or recesses 34 and 36 on its opposite sidewalls. The pairs of slots or recesses 34 and 36 are generally alignedwith the back and front walls, respectively, of the nosepiece structure12.

To slidably mount the workpiece engaging elements 30 and 32 on thenosepiece structure 12, vertically extending leg portions 30B, 32B ofthe members 30, 32 are disposed within the aligned slots or recesses 36,34, respectively. A generally U-shaped closure element or retainingmeans 38 is secured to the nosepiece structure 312, as by a machinescrew 40, with the bight portion of the member 38 overlying the frontwall of the nosepiece structure 12 and with the two legs of the member38 overlying the pairs of slots and recesses 34, 36 to slidably retainthe members 30 and 32 within the slots and recesses. When the elements30, 32 are mounted on the nosepiece structure 12, the workpiece engagingends 30A, 32A of the elements 30, 32 are generally aligned with eachother, considered in the plane of the tool, and are also aligned withthe drive track and the fastener discharge opening in the nosepiecestructure 12. As illustrated particularly in FIGS 4 and 6 of thedrawings, the workpiece engaging portions 30A, 32A are narrower than theadjacent wall of the workpiece engaging surface 12C of the nosepiecestructure 12.

To provide means for coupling the workpiece engaging elements 30 and 32to the safety operator 241, the upper free ends of these elements areprovided with rearwardly, outwardly, and upwardly extending segmentsindicated generally as 30C and 32C which terminate in two laterally andrearwardly extending portions 30D and 32D. The portions 30D and 32Dprovide pivot pins received within two cylindrical sleeves 42A formedintegral with the ends of a lever or coupling member 42. Thus, each ofthe workpiece engaging members 30, 32 is pivotally connected to anopposite end of the lever 42. The lever 42 is provided with a centrallydisposed opening 428 in which is received a reduced diameter orshouldered portion 24A (FIG. 3) on the safety operator 24. A compressionspring 44 interposed between the lower wall of the housing 22 for thecontrol unit 16 and the upper surface of the lever 42 biases theworkpiece engaging elements 30, 32 to their lower or inoperativeposition shown in FIGS. 1 and 2 of the drawings in which the workpieceengaging ends 30A, 32A project below the lower surface 12C of thenosepiece structure I2 to be disposed on opposite sides of or to thefront and back of the drive track extending through the nosepiecestructure 12.

When the tool I0 is to be operated, this tool is moved downwardly towardthe workpiece at the point at which the fastener is to be driven untilsuch time as the workpiece engaging surface 12C of the nosepiece engagesthe adjacent surface of the workpiece. If the tool is disposed in agenerally perpendicular relation with respect to the workpiece, both ofthe workpiece engaging elements 30, 32 are moved from the normalposition shown in FIGS. 1 and 2 to the position shown in FIG. 6. In thisposition, the lower ends of the workpiece engaging portions 30A, 32A aresubstantially flush with the surface 12C of the nosepiece structure 12,and all of these elements are against the adjacent surface of theworkpiece. As the elements 30, 32 move to the position shown in FIG. 6,both ends of the lever 42 are moved upwardly, and this lever compressesthe bias spring 44 during the initial portion of its movement from theposition shown in FIG. 3 to the position shown in dashed outline in FIG.6. This movement is permitted without causing movement of the safetyoperator 24 because of the lost motion connection afforded by thereduced diameter portion 24A of the stem or operator 24. Toward the endof the upward movement of the lever 44, the edges defining the opening428 in the lever 42 engage the upper shoulder of the safety operator 24so that further upward movement of the lever 42 elevates the operator 24to the position shown in FIG. 6. In this upper or operative position,the control unit 16 is in a condition in which actuation of the trigger18 effects the application of power to the power unit so that thefastener supplied by the magazine assembly 14 is driven downwardlythrough the nosepiece structure 12 and into the workpiece.

The construction of the control unit 16 can be such that touch-tripoperation can be provided. This means that the trigger 18 can beoperated, and the surface I2C is then placed against the workpiece toactuate the safety assembly 20 so that the tool 10 operates only afterthe safety is actuated. Alternatively, the safety assembly 20 can befirst actuated followed by the actuation of the trigger 18. Againalternatively, both the trigger l8 and the safety assembly 20 can besubstantially concurrently operated to effect operation of the tool 10.On the other hand, the control unit 16 can be a sequential firearrangement in which the safety assembly 20 must be actuated prior tothe actuation of the trigger 18.

When the tool 10 is lifted from the workpiece, the compression spring 44acts on the lever 42 to move this lever and the connected workpieceengaging elements 30, 32 downwardly to the normal position shown inFIGS. I and 2. During the initial portion of this move ment, the lostmotion connection afforded by the reduced diameter portion 24A permitsthe safety operator 24 to remain in its actuated position. Toward theend of the downward movement of the lever 42 and connected elements 30,32, the lever 42 engages the lower shouldered portion of the operator 24and moves this operator downwardly to its inoperative position. Theprovision of the lost motion connection afforded by the reduced diameterportion 24A tends to reduce multiple firing of the tool 10 arising fromrecoil when the fastener is driven. In other words, a certain returnmovement of the workpiece engaging elements 30, 32 is permitted beforethe safety 24 is actuated to its inoperative position so that continuouspressure forcing the tool I0 against the workpiece does not result inoperation induced by momentary release and reactuation of the safetyoperator 24.

If the tool MI is placed against the workpiece tipped forwardly withinthe plane of the tool, the engaging portion 30A of the element 30engages the workpiece, and the element 30 is moved upwardly to theposition shown in FIG. 4. However, the element 32A either does notengage the workpiece or is only partially actuated thereby with theresult that the lever 42 is tipped to the position shown in FIG. 4. Thismovement of the lever 42 takes up the lost motion provided by thereduced diameter portion 24A on the safety operator 24 and does notcause upwardly directed movement of the operator 24 to its operativeposition in which the control unit 16 is released for operation.Similarly, if the tool is tipped rearwardly within the plane of thetool, the portion 32A of the work engaging member 32 engages theworkpiece, and the member 32 is moved upwardly to its operativeposition, while the front workpiece engaging element 30 remains in itslower position, as shown in FIG. 5. This results in pivoting or tippingthe lever 42 in the opposite direction from FIG. 4. This tippingmovement of the lever 42 is again accommodated by the reduced diameterportion 24A, and even if some upward movement of the safety operator 24takes place, this movement is not sufficient to move the operator 24 toits operative position, and the control unit remains disabled so thatthe tool 10 cannot be operated. Accordingly, when the tool 10 is tippedeither in a forward or a reverse direction about the workpiece engagingsurface 12C generally within the plane of the tool If), only one or theother but not both of the workpiece engaging elements 30, 32 isfully'actuated, and the lever or coupling member 42 is tipped differentdirections but is not elevated sufficiently to shiftthe operator stem 24t'o its operative position. Accordingly, the control unit 16 is notreleased or rendered effective to operate the tool 10.

By providing the point or small area contact portions 30A, 32A forengaging the surface of the workpiece, the tool 10 or, morespecifically, the safety assembly 20 is also able to provide a degree ofcontrol over tipping of the tool 10 in a plane transverse to the planeof this tool. More specifically, if the tool 10 is moved toward theworkpiece in a position inclined to the right or to the left when viewedas shown, for example, in FIG; 6, the tapered or inclined sides ratherthan thepoint of the workpiece engaging portions 30A, 32A tend to firstengage the workpiece to cause initial upward movement of the elements30, 32. However, on continuing movement of the tool 10 toward theworkpiece, one of the side edges of the lower surface 12C of thenosepiece structure tends to engage the workpiece prior to the time atwhich elements 30, 32 are fully elevated to a position in which thelever 42 shifts the operator 24 to its operative position. Only bypivoting the tool 24 to a position in which the surface 12C is flushwith'the workpiece surface can the elements 30, 32 be sufficientlyelevated. If the elements 30, 32 had been provided with the conventionalflat or wide area workpiece engaging surface substantially coextensivewith the width of the lower surface of the nosepiece structure, theelements 30, 32 would be fully actuated by moving the tool l toward theworkpiece with this tool tipped to either side, as viewed for example inFIG. 6.

In summary, the improved safety assembly of the present inventioninsures that the tool is flush against a workpiece before the tool canbe operated. Further, by providing the elements and 32 on opposite sidesof the drive track, the tool Ml cannot be operated if the fastenerdischarging opening is not covered by a workpiece because one of theelements 30 and 32 would not be actuated. In addition, the provision oftwo workpiece engaging elements 30 and 32, both of which must beactuated for operation of the tool 10, reduces the possibility of afailure of the safety due to the workpiece engaging element being lockedin an operated state by, for example, an accumulation of foreign matterin a guideway.

Although the present invention has been described with respect to asingle illustrative embodiment thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art which fall within the spirit and scope of theprinciples of this invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. In a fastener driving too] having a power unit for driving fastenersinto a workpiece,

nosepiece structure through which the fasteners are driven and having aworkpiece engaging portion,

a control unit for controlling the power unit and having an operatormeans movable between an inoperative position and an operated positionin which the control unit can effect operation of the power unit,

a pair of workpiece engaging means independently movable relative to thenosepiece structure and disposed adjacent opposite sides of theworkpiece engaging portion thereof,

and coupling means coupling the pair of workpiece engaging means to theoperator means and operable to shift the operator means from itinoperative position to its operated position only when both of theworkpiece engaging means are moved by engagement with the workpiece.

2. The fastener driving tool set forth in claim 1 in which at least oneof the workpiece engaging means is formed with a pointed or narrowworkpiece engaging surface that provides a point or small area ofcontact with the workpiece aligned with the path of movement of thefasteners through the nosepiece structure.

3. The fastener driving tool set forth in claim 2 in which the nosepiecestructure includes a workpiece engaging surface that is wider than theworkpiece engaging surface on the workpiece engaging means.

4. The fastener driving tool set forth in claim l in which the couplingmeans includes a lever means engaged by the operator means at a firstpoint and engaged by the workpiece engaging means at spaced second andthird points.

5. The fastener driving tool set forth in claim 4 in which the secondand third points are spaced on opposite sides of the first point.

6. The fastener driving tool set forth in claim 4 in which the secondand third points are at the ends of the lever means,

and the coupling means includes means providing a fixed pivotalconnection between the lever means and the workpiece engaging means atthe ends of the lever means.

7. In a fastener driving tool using a power unit for actuating a driverelement,

a nosepiece structure through which fasteners are driven by the driverelement, said structure including a workpiece engaging structure adaptedto be disposed adjacent a workpiece,

a control unit for controlling the operation of the power unit, saidcontrol unit including a manually operable trigger means and a safetyoperator,

a pair of workpiece engaging means mounted adjacent opposite sides ofthe workpiece engaging structure for independent movement,

and linkage coupling both of the workpiece engaging means to the safetyoperator and operable to actuate the safety operator only when both ofthe workpiece engaging means are moved by engagement with the workpiece.

8. The fastener driving tool set forth in claim 7 in which the linkageincludes a lever means coupled to the safety operator and having apivotal engagement with each of the workpiece engaging means.

9. The fastener driving tool set forth in claim 8 in which the linkageincludes means providing a pivotal connection between opposite endportions of the lever means and separate ones of the pair of workpieceengaging means.

10. In a fastener driving tool with a power unit for driving fastenersinto a workpiece,

a housing for the fastener driving tool,

a control unit on the housing for controlling the operation of the powerunit to drive a fastener, said control unit including an operator meansdepending from the control unit, said operator means being normally inan inoperative position and being movable upwardly to an operativeposition to permit operation of the tool,

a movably mounted coupling member beneath the control unit and adaptedto engage and move the depending operator means from its inoperativeposition to its operative position, said coupling member and operatormeans being engageable at a first point on the coupling member spacedfrom its opposite ends,

a first member slidably mounted on the housing beneath the couplingmember for movement between a lower inoperative position and an upperoperative position in which the first member elevates one end of thecoupling member,

and a second member slidably mounted on the housing beneath the couplingmember for movement between a lower inoperative position and an upperoperative position in which the second member elevates the other end ofthe coupling member, the elevation of both ends of the coupling memberby the first and second members elevating the coupling member to engageand move upwardly the operating means thereby to render the control uniteffective to operate the power unit.

1. In a fastener driving tool having a power unit for driving fastenersinto a workpiece, nosepiece structure through which the fasteners aredriven and having a workpiece engaging portion, a control unit forcontrolling the power unit and having an operator means movable betweenan inoperative position and an operated position in which the controlunit can effect operation of the power unit, a pair of workpieceengaging means independently movable relative tO the nosepiece structureand disposed adjacent opposite sides of the workpiece engaging portionthereof, and coupling means coupling the pair of workpiece engagingmeans to the operator means and operable to shift the operator meansfrom it inoperative position to its operated position only when both ofthe workpiece engaging means are moved by engagement with the workpiece.2. The fastener driving tool set forth in claim 1 in which at least oneof the workpiece engaging means is formed with a pointed or narrowworkpiece engaging surface that provides a point or small area ofcontact with the workpiece aligned with the path of movement of thefasteners through the nosepiece structure.
 3. The fastener driving toolset forth in claim 2 in which the nosepiece structure includes aworkpiece engaging surface that is wider than the workpiece engagingsurface on the workpiece engaging means.
 4. The fastener driving toolset forth in claim 1 in which the coupling means includes a lever meansengaged by the operator means at a first point and engaged by theworkpiece engaging means at spaced second and third points.
 5. Thefastener driving tool set forth in claim 4 in which the second and thirdpoints are spaced on opposite sides of the first point.
 6. The fastenerdriving tool set forth in claim 4 in which the second and third pointsare at the ends of the lever means, and the coupling means includesmeans providing a fixed pivotal connection between the lever means andthe workpiece engaging means at the ends of the lever means.
 7. In afastener driving tool using a power unit for actuating a driver element,a nosepiece structure through which fasteners are driven by the driverelement, said structure including a workpiece engaging structure adaptedto be disposed adjacent a workpiece, a control unit for controlling theoperation of the power unit, said control unit including a manuallyoperable trigger means and a safety operator, a pair of workpieceengaging means mounted adjacent opposite sides of the workpiece engagingstructure for independent movement, and linkage coupling both of theworkpiece engaging means to the safety operator and operable to actuatethe safety operator only when both of the workpiece engaging means aremoved by engagement with the workpiece.
 8. The fastener driving tool setforth in claim 7 in which the linkage includes a lever means coupled tothe safety operator and having a pivotal engagement with each of theworkpiece engaging means.
 9. The fastener driving tool set forth inclaim 8 in which the linkage includes means providing a pivotalconnection between opposite end portions of the lever means and separateones of the pair of workpiece engaging means.
 10. In a fastener drivingtool with a power unit for driving fasteners into a workpiece, a housingfor the fastener driving tool, a control unit on the housing forcontrolling the operation of the power unit to drive a fastener, saidcontrol unit including an operator means depending from the controlunit, said operator means being normally in an inoperative position andbeing movable upwardly to an operative position to permit operation ofthe tool, a movably mounted coupling member beneath the control unit andadapted to engage and move the depending operator means from itsinoperative position to its operative position, said coupling member andoperator means being engageable at a first point on the coupling memberspaced from its opposite ends, a first member slidably mounted on thehousing beneath the coupling member for movement between a lowerinoperative position and an upper operative position in which the firstmember elevates one end of the coupling member, and a second memberslidably mounted on the housing beneath the coupling member for movementbetween a lower inoperative position and an upper operative position inwhich the second member elevates the other end of the Coupling member,the elevation of both ends of the coupling member by the first andsecond members elevating the coupling member to engage and move upwardlythe operating means thereby to render the control unit effective tooperate the power unit.